Since an organic Electro Luminescence (EL) element is a self-light-emitting element of a current driven type, the need for a backlight is eliminated while the advantage of low power consumption, high viewing angle, high contrast ratio or the like is obtained; it is expected to perform well in the development of a flat panel display.
In an organic EL display device using such an organic EL element, subpixels of different colors of red (R), green (G) and blue (B) are used to constitute a large number of pixels, which makes it possible to display various kinds of color images. While these subpixels of R, G, and B (RGB) may be located in various different forms, they are generally arranged in stripes by equally placing subpixels of different colors (so-called RGB vertical stripe arrangement), as illustrated in FIG. 1. All colors can be displayed by adjusting the brightness among the three subpixels. In general, adjacent three subpixels of R, G and B are collectively regarded as one rectangular pixel, and such rectangular pixels are arranged in a square to realize a dot matrix display. In the display device of a dot matrix type, image data to be displayed has a matrix arrangement of n×m. A correct image can be displayed by associating the image data with each pixel one for one.
Furthermore, organic EL devices have different structures including a color filter type which creates the three colors of RGB with a color filter on the basis of a white organic EL element, and a side-by-side selective deposition type which deposits different colors on the respective organic EL materials for the three colors of RGB. While the color filter type has a disadvantage in that the light use efficiency is lowered as the color filter absorbs light, resulting in higher power consumption, the side-by-side selective deposition type can easily have wider color gamut due to its high color purity and can have higher light use efficiency because a color filter is eliminated, thereby being widely used.
In the side-by-side selective deposition type, Fine Metal Mask (FMM) is used in order to individually color organic EL materials. It is, however, difficult to fabricate FMM because pitches thereof are made finer to be adapted for recent highly-refined organic EL display devices. To address such a problem, using the characteristics of human color vision, i.e. human eye being insensitive to R and B whereas sensitive to G, a pixel arrangement structure in which subpixels are constituted with two colors of G and B, or G and R, and a color expression requiring a subpixel of a missing color compared to the RGB arrangement is reproduced into a pseudo array by combining the two-color subpixels with an adjacent pixel having a subpixel of the missing color (so-called PenTile (registered trademark) arrangement) has been proposed (U.S. Pat. No. 6,771,028, US Patent Application Publication No. 2002/0186214, US Patent Application Publication No. 2004/0113875 and US Patent Application Publication No. 2004/0201558, for example).
The PenTile arrangement causes a dot width for R and B corresponding to two vertical stripes, reduces the number of subpixels, allows the aperture size of FMM to be larger and thus facilitates the manufacturing of a highly refined organic EL display device. However, the PenTile arrangement uses the tiling method to alleviate a color failure due to reduction in the number of subpixels. Therefore, the PenTile arrangement causes a jaggy in which curve lines of an image to be displayed smoothly are displayed in a staircase pattern, or a defect in which color changes are viewed as lines in an image with continuously changing color tone or luminance.
In the background as described above, a pixel arrangement structure which can increase the dimension of a subpixel compared to the conventional RGB vertical stripe arrangement and which causes less degrading in display quality as in the PenTile arrangement has been proposed. This structure is a pixel arrangement structure (so-called “S stripe arrangement”) in which R and G are located in the same column while B is located in the column subsequent to R and G, as well as in the row of R and G, as illustrated in FIG. 3 (Japanese Patent Application Laid-Open Publication No. 2011-249334, for example). This S stripe arrangement allows the width of a subpixel to be wider than that in the RGB vertical stripe arrangement, which can increase the aperture size of FMM and can also enhance the display quality compared to the PenTile arrangement because subpixels of RGB are located in one pixel.